1. Field of the Invention
This invention relates to a signal separator and a bandpass filter that are capable of handling high power radio frequency (rf) signal energy in television broadcast antenna installations.
2. Description of the Prior Art
The advent of digital television (DTV) has resulted in a need for a station to broadcast both a national television standard code (NTSC) signal for reception by NTSC sets and a DTV signal for reception by DTV sets. A common practice is to mount a DTV antenna to the existing tower upon which is mounted the NTSC antenna. A single transmission line extends up the tower for the purpose of feeding the NTSC signal from a transmitter to the NTSC antenna. Although the transmission line may be either a waveguide or a coaxial structure, a coaxial structure is preferred because of the additional wind loading on the tower and group delay distortion on the signal that results from a waveguide structure.
A separate transmission line could be added to feed the DTV signal up the tower to the DTV antenna. However, it is preferable to use the single existing transmission line to feed both the NTSC and the DTV signals to their respective antennas as this is less expensive and does not add wind load. For example, U.S. Pat. No. 5,774,193 uses a signal combiner to combine the NTSC and DTV signals to form a composite signal that is fed up the transmission line. A signal separator disposed at the upper end of the transmission line separates the composite signal into the DTV signal and NTSC signal for application to the DTV and NTSC antennas. The signal separator is formed of a high pass filter and a low pass filter. The high pass filter passes an ultra high frequency (UHF) DTV signal to the DTV antenna, but rejects a very high frequency (VHF) NTSC signal. The low pass filter passes the VHF NTSC signal to the NTSC antenna, but rejects the UHF DTV signal. The high and low pass filter separator may provide adequate bandwidth and rejection for the case of the DTV signal and the NTSC signal being in two different frequency bands. However, it does not provide adequate rejection for the case where the carrier frequencies of the two signals are relatively close together as, for example in the same frequency band.
Accordingly, there is a need for a signal separator that has adequate bandwidth and rejection for the case where the carrier frequency difference of signals to be separated is relative small. There is also a need for filter assemblies that can be used in such a separator.